Phase-balancing system.



R. E. HELLMUND.

PHASE BALANCING SYSTEM.

APPLICATION FILED AUG. I0, 1916.

1,281,956. Patented 0ct.15, 1918..

3 SHEETS-SHEET I- WITNESSES:

15m (W%M.

R. E. HELLMUND.

PHASE BALANCING SYSTEM.

APPLlCATlON FILED AUGJO. I916.

Patented Oct. 15, 1918.

3 SHEETS-SHEEI 2.

- 0 muuuno omooogoo INVENTOR A zORNEY R. E. HELLMUND.

PHASE BALANCING SYSTEM. APPLICATION FILED AUG. 10. ms.

1,281,956. Patented 00t.15, 1918.

3 SHEETS-SHEET 3.

' 8 Lemon-99mm 000M000 J WITNESSES: INVENTOR 244 Rudolf E Hal/Mona UNITED sTA'rEs PATENT OFFICE. A

:aUnoLF E. HELLMUND, or SWISSVALE, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION or PENNSYLVANIA.

PHASE-BALANCING SYSTEM.

Application filed August 10, 1916.

To {(U7177101)} it may concern:

Be it known that I, RUDoLF 'E. HELL- MUNI), a. subject of the Emperor of Germany,and a resident of Swissvale, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Phase-Balancing Systems, of which the following is a specification.

My invention relates to systems of alternating-current distribution, more particularly of that character wherein three-phase currents are derived from a single-phase source by means of a phase-converter, and it has for its object to provide means whereby the unbalancing and distortion of the three-phase load circuit, caused by impedance drops within the phase-converter, may be compensated for and a condition of balance maintained in the three-phase load circuit under all conditions of load.

Referring to the accompanying drawing, Figure 1 is a diagrammatic view of an alternating-current system of distribution of the character above designated, together with means, operative in accordance with my invention, for maintaining a balance therein; Fig. 2 is a vector diagram representing the voltage relations in the system of Fig. 1 under the various conditions of operation; and Figs. 3 to 7, inclusive, are diagrammatic views of modifications of the system shown in Fig. 1.

In the operation of alternating-current railways, it is desirable to employ a singlephase, high-voltage trolley for simplicity and economy of transmission but it is desirable to employ poly-phase induction. motors for propulsive purposes on account of the ruggedness and desirable operating characteristics thereof. A phase-converter of the rotary type is therefore mounted on the vehicle for the purpose of deriving the three-phase propulsive current from the single-phase supply.

It is a well known fact that, in a phaseconverter of the character designated, the efi'ect of the impedance of the various parts of the winding is to produce an alteration in the magnitude and phase relation of the secondary induced voltage with respect to the primary impressed voltage, with resultant distortion and unbalaneing of the threephase electromotive forces supplied to the motors. When motoring, the effect of said drops is to reduce the output voltage of the Specification of Letters Patent.

Patented Oct. 15, 1918.

Serial No. 114,167.

phase-converter and, when recuperating, the effect is to unduly increase said output voltage.

By my invention, I provide motive means which are in a state of equilibrium when the output voltage of the phase-converter is substantially 87% of the supply-impressed voltage and which are operative, when said 87% relation is disturbed, to adjust the voltage supply to the primary winding of the phase-converter to such an amount as to restore said 87% relation. In like manner, I provide motive means which are in a state of equilibrium when the two derived threephase electromotive forces are balanced and which are operative, when said voltages become unequal, to shift the point of attachment ofthe terminal of the secondary winding of the phase-converter to the primary source to such an amount as to restore a balance between two said derived voltages. By the joint action of said two motive means, the magnitude and the phase relation of the various voltages in an alternating-current system of the character designated may be maintained as desired, throughout wide changes of load, whether propulsive or recuperative.

Referring to Fig. 1 of the accompanying drawing for a more detailed understanding of my invention, I show the secondary winding of a supply transformer at 8. Said winding may be a portion of a two-winding transformer or may be a secondary winding of an auto-transformer, the particular type of apparatus used in this relation consti tuting no part of my invention and therefore needing no further mention. Current is supplied from the two terminals of the winding 8 to two terminals of a three-phase propulsive motor 9, of the induct-ion type, by means of suitable leads 10 and 11. The primary winding 12 of a phase-converter 13, of the rotary type, is connected between the left-hand terminal of the secondary winding 8 and a tap 14.- adjacent the right-hand terminal of said winding. The secondary winding 15 of the phase-converter 13 is con nected between a tap 16 adjacent the mid point of the winding 8 and the remaining terminal of the motor 9.

,A balanced relay 17 is provided for moving the tap '16 and includes two opposing windings 18 and 19. The winding 18 is connected between the left-hand terminal of the source 8 and the lower terminal of the secondary winding of the phase converter 13 and, in like manner, the winding 19 is connected between the right-hand terminal of the source 8 and said phase-converter terminal. Under normal operating conditions, the forces exerted by the solenoids 18 and 19 upon the core of therelay l7 balance each other, and the tap 16 remains stationary.

An additional relay 20 includes two windings 21 and 22, the former of which is con nected between the terminals of the supply winding 8 and the latter of which is connected between the midpoint of said winding 8 and the lower terminal of the secondary winding 15 of the phase-converter 13. The force developed by the solenoid 21 opposes that developed by the solenoid 22, and the relative numbers of turns in the two solenoids are so adjusted that, when the voltage generated in the secondary winding 15 is substantially 87% of the voltage of the supply winding 8, said solenoids neutralize each other in their effect upon the core of the relay 20, and the tap 14 remains stationary.

Having thus described the structure of a system embodying my invention, the operation is asfollows. Referring to Fig. 2, the voltage of the supply winding 8 is plotted as a vector 23-2% and the voltage of the secondary winding 15 of the phase converter is plotted as a vector 25-26. The voltage 25-26 is adjusted to substantially 87% of the supply Voltage and has a quadrature relation thereto, and the upper terminal of the winding 15 is connected to substantially the mid point of the supply winding 8, so that the point 26 forms the vertex of an equilateral triangle of which the vector 23-24 forms the base, as is well known and understood in connection with the Scott or T connection for transformers. Under the conditions assumed, the three-phase voltages supplied to the motor 9 may be represented by the vectors 23-24, 21-26 and 26-23. The effect of the impedance drops in the various parts of the system, when load comes upon the motor 9, is to cause a change in the phase and magnitude of the output voltage of the phase converter. To illustrate this action, the vector 25-26 may be assumed to take the position and magnitude indicated by the vector 25-27. The point 27 now becomes the vertex of the threephase delta, and the resultant unbalanced electromotive forces supplied to the motor 9 have an extremely undesirable effect upon the operating characteristics thereof, as is well known. It becomes necessary, therefore, to move the point 27 to coincidence with the point 26. The vector 23-27 is unequal to the vector 24-27 and the balance of the relay 17 is, therefore, destroyed, the winding 19 overpowering the winding 18 and moving the tap 16 to the right, tending to cause the vector 2527 to move parallel to itself and to assume a position 28-29 in which it points directly at the desired vertex 26. The vector 25-27 is less than 87 of the vector 23-24 so that the winding 21 overpowers the winding 22, moving the tap 1a to the right and increasing the primary impressed voltage of the phase converter 13. There immediately follows a corresponding increase in the secondary or induced voltage of the phase converter, resulting in an increase in the length of the vector- 28-29 until the point 29 coincides with the point 26. The electromotive forces supplied to the motor 9 have thus been restored to their original equality in spacing and magnitude,

as is deslred for proper operation.

During recuperation, an analogous regulating operation is effected by the apparatus disclosed. The vector 25-26, representing the voltage of the phase-converter secondary winding 15, is altered in phase and increased in magnitude so that it assumes a position 25-30. This vector tends to move parallel to itself by the action of the relay 17, in shifting the tap 16, until it assumes the position 31-32'and it is then diminished in adapt motors for the operation of the regulating devices, as indicated in Fig. 3. The main elements of the system of distribution itself are as shown in Fig. 1, and like elements are similarly numbered. The tap 16 is rendered subject to control by a rack-andpinion mechanism 33 which, in turn, is driven by two motors 34 and 35 which normally oppose each other in torque. The exciting field winding of the motor 34 is connected between the left-hand terminal of the source 8 and the outer terminal of the phase-converter secondary winding 15 and, in like manner, the field winding of the motor 35 is connected between the tap 1+1 and said outer point. Thus, the voltages impressed upon the field windings of the two motors are represented by the vectors 21-26 and 23-26, respectively, in Fig. 2. The armatures of the motors 34 and 35 are connected in series across the source 8 so that the voltage impressed thereupon may be represented by the vectors 25-21 and 23-25, respectively. Both the armature and field circuits are, arranged to have the same relation between reactance and resistance so that the relative. phase relation of the fields and currents therein is the same as those of the impressed voltages. Thus the torques developed within the motor 34: may be measured by the product of the vectors and 24-26 multiplied by the cosine of the intervening angle, and in. like manner, the torque of the motor may be represented by the, product of the vectors 28 25 and 23-26 into the cosine of their intervening angle. Under the condition of initial or noload equilibrium. represented by the full-line, triangle 23'2426, the opposing torques of the motors 34.35 are equal and, therefore, the adjusting apparatus for the tap 16 is in equilibrium. The effect of load on the. motor 9 is to cause the vector 2526 to assume the position 25-27, producing an unbalanced three-phase supply for the motor 9. There follows an unbalanced of the torques in the two motors 34k and 35 which results in a movement of the tap 16 toward the right, causing the vector 25-127 to as sume the position 2829, as previously described.

The. tap 14 is also subject to the control of two motors 37, and- 38 through a rackand-pzinion mechanism 39, each. of said motors being of the series commutating type and the motor 37 being connected between I the. left-hand terminal of the supply winding 8 and the tap 14, whereas, the motor 38 isconnected across the winding 15. Thus, the motor 37 is energized in accordance with the length of the vector 23-,2;l, whereas, the motor 38 is energized in accordance with the length of the vector .2526. The number of turns in said motors is so adjusted that their opposing torques balance each other when the vector 2.526 has the desired 87% relation to the vector 23-24. The, lowering of the voltage of the winding 15, because of the impedance drops within the system, with resultant reduction of the vector 2526 to the value 28- 29, destroys the equilibrium between the motors 37 and 38, producing movement of the tap 14 to the right, increasing the primary voltage and, accordingly, the secondary voltage of the phase-converter 13 until the point 29 is moved into coincidence with the point 26.

The analogous operation takes place during recuperation to maintain the balance of thethree-phase system, all as described in connection with Fig. 1.

In the description'of the operation of the systems of both Fig. 1 and Fig. 3, I have assumed, for purposes of clearness, that one corrective device performs its entire opera tion. before the inception of movement by the other, but, as a matter of fact, the operating mechanisms for the taps 14 and 16 move simultaneously and, therefore, the

point 27 in reality moves directly toward the point 26 and not via the point 29. This feature of the operation should be borne carefully in mind, as the passage of the point 27 to the other side of the vector 2526, to some such position as the point 29, involves a reversal in the relative magnitudes of the two derived three-phase voltages and a consequent reversal and uncertainty in operation of the control apparatus subject to said two voltages. It is unnecessary to employ two distinct motors of opposing torque in each regulating device, as their function may be performed by a motor having a single armature and two distinct field windings the torques of which oppose each other. A structure of this type is shown in Fig. 4 wherein the main elements of a phase-converter sys-v tem are shown and designated as heretofore. The adjusting mechanism for the tap 16 comprises a single motor 40 which is provided with two exciting field windings 4L1 and 42 connected respectively across the voltages represented by the vectors 2326 and 24L26 in Fig. 2. The. armature of the motor 40 is connected across the sourcev 8', with an appropriate, phase-adjusting device 4-3 in circuit therewith, and also, if desired, an inducing field winding 44. Special care should be taken to avoid mutual induction betweenv the field windings 41 and 42 and, to this end, they should be mounted upon distinct pole extensions. The torques produced by said two field windings oppose each other and are in equilibrium, under a condition of balance in the three-phase circuit, and one overpowers the other for the adj ustment of the tap 16 under conditions of unbalance in the three-phase circuit, as mentioned in connection with the motors 34 and 35 in the system of Fig. 3. In like manner, the function of the motors 37 and 38 of Fig. 3 is performed by a single motor-45 having two exciting field windings 46 and 47. The armature of the motor 45 and the field winding 46 are connected in parallel relation with each other across the source 8, a resistor 48 being included in series with the former and a resistor 49 in series with the latter. The exciting field winding 47 is con nected across the winding 15 of the phase converter through a reactive device 50. The current in the field winding 415 is substantially in phase withthe supply voltage if the resistor 4:9 is relatively high, as compared with the inductance of the circuit. The same is true with regard to the armature current. The current in the field winding 47 lags substantially 90 behind the voltage of the winding 15 and, therefore, lags substantially 180 behind the voltage of the source 8 if the inductance of the device 50 is large relative to the resistance of said field circuit. The resultant field of the mo tor 45 may, therefore, be adjusted to substan tially a zero value when the output voltage of the phase converter is substantially 87% of the supply voltage, by appropriate adjustment of the number of turns in each field winding, because of this 180 phase relationship. A departure from the desired 87% relation of the supply and phase-converter secondary voltage, however, produces an unbalanced torque in the motor 45, with resultant appropriate movement of the tap 14.

The system of Fig. 5 is broady similar to those hitherto described but the adjusting motor 40 for the tap 16 is provided with a single exciting winding 51 which is connected between the mid-point of the source 8 and the outer terminal of the winding 15 through a resistor 52. The armature of the motor 40 is connected across the source 8, as before, through a resistor 53. The resistors 52 and 53 are of relatively high value so that the currents in the armature and exciting field winding of the motor 40 are sub stantially in line with the voltages impressed thereupon. When the vector 2526 is perpendicular to the vector 23-24, in Fig. 2, therefore, no torque is developed within the motor 40 and there is no tendency to move the tap 16. When the voltage 25-26 of Fig. 2' departs from its 90 relationship to the voltage 23-24, however, in either direction, torque is developed within'the motor 40, and appropriate adjustment is made at the tap 16. The motor 45, for the adjustment of the tap 14, is energized as in Fig. 4 except that the armature thereof is supplied with the resultant of the field currents of the exciting windings 46 and 47. It is not necessary therefore that the current in the field winding 47 be shifted as much as before by the inductive device 50 because the phase of the armature current is between the phases of the two exciting field currents and there is no resultant torque if the fields are equal. It should be noted that but onehalf the voltage of the supply 8 is used for the field winding 47, which necessitates that adjustment be made for zero torque when the voltage impressed upon the circuit of the field winding 46 is substantially 174% of the voltage impressed upon the field winding 47.

The two component voltages which, because of relative nil-balancing, cause adjustment of the taps in systems of the character heretofore described, may be induced in a single circuit by means of transformers and adjusting mechanism operated by the net or resultant current produced in said circuit. A system of this character is shown in Fig. 6 wherein the operating motor 40 for the adjustment of the tap 16 is provided with a single exciting field winding 51 in circuit with a resistor 52 and with the secondary "windings 54 and 55 of two transformers on and 57. The primary windings of said transformers are connected to beenergized by the voltages 2326 and 24 26 of Fig. 2, respectively. The voltage impressed upon the armature of the motor 40 is derived from the secondary winding 58 of a transformer 59, the primary winding of which is connected across the supply 8, rather than connecting said armature directly to said supply.

In like manner, the operating motor 45 for the tap 14 is provided with a single exciting winding 60 which derives its energy from the secondary windings 61 and 62 of transformers 63 and64, the former of which has its primary winding connected across the supply 8 through a resistor 65 and the latter of which has its primary winding connected between the mid point of the primary winding of the transformer 59 and the outer terminal of the generating winding 15 of the phase-converter 13 through a reactor 66. Thus, by proper adjustment of the number of turns, the motor 45 may be rendered inactive when the desired 87% relationship is present in the T connection but isrendered active to adjust the tap 14 when said 87% relationship is disturbed. The use of auxiliary transformers, as shown, not only simplifies the field windings of the motors but it also permits the reduction of the supplv voltages to amounts more suitable for relay operation.

The system of Fig. 7 is similar to those previously shown except that an auxiliary auto-transformer 67 is employed to obtain a point of connection for the various circuits which shall be at the potential of the mid point of the supply.

In various of the systems above discussed, I have shown, for simplicity and clearness, a relay motor as operating the 'tap through a rack-and-pinion mechanism. It will be understood, however, that, in commercial practice, particularly in heavy traction work, the relay motors may operate a pneumatically controlled head which, by suitable contact members, operates unit switches, as is well known in the control art.

While I have shown my invention in a plurality of forms, it will be obvious to those skilled in the art that it is susceptible of various minor changes and modifications without departing from the spirit thereof and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are indicated i the appended claims.

I claim as my invention:

, 1. The combination with a source of single-phase currents, of means for deriving therefrom a quadrature-related electromotive force of substantially 87% the magnitude thereof, connections for combining said two electromotive forces to form a T, connections for deriving substantially balanced three-phase electromotive forces from said T, means responsive to a deviation from said 87 relation and operative to restore the same, and means responsive to an inequality between the two derived three-phase electromotive forces and responsive to restore equality therebetween.

2. The combination with a source of single-phase, alternating currents, of a phaseconverter operative to derive therefrom a quadrature related electromotive force of substantially 87% of the magnitude thereof, connections for combining said two electromotive forces to form a T, connections for supplying a variable three-phase load from said T, means responsive to'a deviation from said 87% relation and operative to restore the same, and means responsive to an inequality between the two, derived, threephase electromotive forces and operative to restore equality therebetween.

3. The combination with a source of single-phase, alternating currents, of a phaseconverter operative to derive therefrom a quadraturerelated electromotive force of substantially 87% of the magnitude thereof, connections for combining said two electromotive forces to form a T, connections for supplying a variable three-phase load from said T, means responsive to a deviation from said 87% relation and operative to adjust the output voltage of said phase-converter to restore said relation, and means responsive to an inequality between the two derived three-phase electromotive forces and operative to shift the point of attachment of the stem to the head of said T to restore equality between said derived electromotive forces.

4. The combination with a source of single-phase, alternating currents, of a phaseconverter operative to derive therefrom a quadraturerelated electromotive force of substantially 87% of the magnitude thereof,

" connections for combining said two electromotive forces to form a T, connections for supplying a variable three-phase load from said T, motor means operative 1n accordance with the voltage of'the primary source, op-

posing motor means operative in accordance with the voltage of said quadrature-related source, said two motor means balancing each other when said 87 relation is present and one overbalancing the other to adjust the output voltage of said phase-converter when said 87 relation is destroyed to restore the Copies of this patent may be obtained for same, and means responsive to an inequality between the two derived three-phase electromotive forces and operative to restore equality therebetween.

5. The combination with a source of sin gle-phase, alternating currents, of a phaseconverter operative to derive therefrom aquadraturerelated electromotive force of substantially 87 of the magnitude thereof, connections for combining said two electromotive forces to form a T, connections for supplying a variable three-phase load from said T means responsive to a deviation from said 87% relation and operative to adjust the output voltage of said phase-converter to restore said relation, and two opposing motor agencies, one of which is connected to be energized from each of the two derived three-phase electromotii e forces, said motor agencies balancing each other when said voltages are equal and being operative to shift the point of attachment of the stem to the head of said T to restore equality between said electromotive forces when said equality is destroyed.

6. The combination with a source of single-phase, alternating currents, of a phaseconverter operative to derive therefrom a quadraturerelated electromotive force of substantially 87 of the magnitude thereof, connections for combining said two electromotive forces to form a T, connections for supplying a. variable three-phase load from said T, motor means operative in accordance with the voltage of the primary source, opposing motor means operative in accordance with the voltage of said quadrature-related source, said two motor means balancing each other when said 87% relation is present and one overbalancing the other to adjust the output voltage of said phase-converter when said 87% relation is destroyed to restore the same, and two opposing motor agencies, one of which is connected to be energized from each of the two derived three-phase electromotive forces, said motor agencies balancing each other when said voltages are equal and being operative to shift the point of attachment of the stem to the head of said T to restore equality between said electromotive forces when said equality is destroyed.

In testimony whereof, I have hereunto subscribed my name this 28th day of July,

RUDOLF E. HELLMUND.

flve cents each, by addressing the "Commissioner of Patents.

Washington, D. G. 

